Fire Ant Outcompetes Other SpeciesEven in its
Native Habitat

Even in its native Argentina, the fire
ant wins in head-to-head competition with other ant species more than
three-quarters of the time, according to Agricultural Research Service (ARS)
scientists.

ARS scientists at the
South
American Biological Control Laboratory (SABCL) in Hurlingham, Argentina,
have been studying how different ant species fare against the fire ant as part
of an effort to learn more about the behavior of this pestan invasive
species in its non-native United States.

Fire ants often attack in swarms--not only causing painful stings to humans,
but can even kill small animals. Little has been known, however, about the fire
ant's competitive nature or how it interacts with other ants.

SABCL biologist Luis Calcaterra, working closely with lab director
Juan
Briano, has been studying interactions between the red imported fire ant,
Solenopsis invicta, and other aboveground foraging ants in two habitats
in northeastern Argentinausing a combination of pitfall traps and baits
to study day-to-day activity in ant communities.

The pitfall trap is a 50 milliliter plastic tube buried in the ground and
half-filled with soapy water. The bait is one gram of canned tuna placed on a
plastic card measuring five centimeters in diameter. The trap and bait gave the
scientists a way to determine ant populations at the sites, and showed the
dominance of each species.

Some 28 ant species coexisted with S. invicta in an open area of
forest growing along a watercourse, whereas only 10 species coexisted with S.
invicta in the dry forest grassland. The researchers found that the fire ants
had the highest numbers in the open forest area along the watercourse.

Prior to these studies, it was thought that the fire antnow
established throughout the Americaswas not dominant in its native land.
But the studies showed that the fire ants were the most ecologically dominant,
winning 78 percent of the interactions with other ants, mostly against its most
frequent competitor, the South American big-headed ant, Pheidole
obscurithorax, an ant of northern Argentina and Paraguay also introduced in
the United States. And in battles with the invasive Argentine ant,
Linepithema humile, the fire ants were even more dominant, winning out
80 percent of the time.

This study was published in Oecologia, a journal
that deals with plant and animal ecology.

Read
more about the research in the July 2009 issue of Agricultural
Research magazine.